It is well known in the prior art to fabricate a temperature sensor using a conductive material whose resistance changes with temperature. By determining the resistance of the sensor it is possible to determine the temperature of the environment in which the sensor is positioned. Such a technique is known, for example, for use in a temperature probe for monitoring oven temperature. The sensed temperature is used in a feedback or closed loop control circuit for maintaining the oven temperature at a desired setpoint.
U.S. Pat. No. 4,159,459 to Sease et al. discloses a thin film cylindrical resistor. A cylindrical insulating substrate has an electrically conductive coating which is selectively cut along an axial path to form a spiral disruption. This increases the resistance of the conductive material in a region between two metal contacts on the resistor. The cutting is preferably accomplished with a laser beam and as noted at column 3 of the '459 patent, "the degree of rotation while the laser beam is off may, of course, be varied to vary the gap in the spiral cut depending upon the size and the desired characteristics of the resistor."
U.S. Pat. No. 4,670,734 to Caddock discloses a thick film resistor fabrication technique having a substrate of insulating material which supports a thick film conductive resistor. A laser is used to form a zig-zag path of conductive material spaced by the insulating material. The shape of the zig-zag path is controlled to avoid inductive effects accompanying the energization of the path during use of the resistor.
U.S. Pat. No. 4,881,057 to Garcia et al. which issued Nov. 14, 1989 and is assigned to the assignee of the present invention discloses a temperature sensor. This sensor is used in con]unction with control apparatus for defrosting a refrigeration coil. Two thick film resistor elements are mounted on a substrate and a thermistor coupled to those elements to form a voltage divider. The resistance of the thermistor is determined at a reference temperature and the thick film resistor elements are precisely trimmed using a laser trimmer. The disclosure of the '057 patent to Garcia et al. is incorporated herein by reference.